The invention relates to sensing apparatus for use with capacitive presence detection systems.
Motion detection systems are known for detecting the presence of a person or vehicle to a device such as a parking gate. One type of system that utilizes the rate of change in frequency of a signal from an oscillation from a continuous wave output is disclosed in U.S. Pat. No. 5,337,039 to Simon. The system utilizes an oscillator which produces a wave in a preset frequency range which is delivered to a capacitive plate or sensor. The sensor is mounted to a device such as a parking gate. The sensor is in the form of a coaxial cable which functions as one plate of a capacitor. The cable is attached by clips to the gate. When the sensor nears conductive objects, the frequency of the preset signal changes. An error signal is generated if the rate of change in frequency exceeds a predetermined rate. The error signal is sent to a control unit which emits a signal to stop the movement of the gate. If the gate is wood, the sensor is affixed to the bottom of the gate. However, if the sensor is used with a metal object such as a garage door, the sensor cannot be attached directly to the metal without drastically reducing the capacitive field and thus the range of the detection.
It is an object of the invention to provide sensing apparatus for use with capacitive presence sensing detection which provides easy installation. It is also an object of the invention to provide a sensor with a proper field of detection when mounted to conductive objects such as metal doors and gates.
The invention relates to improvements in capacitive sensors and spacers for improving the depth of field of capacitive presence sensing systems. In one embodiment suited for use with a wooden substrate such as a parking gate, the sensor is a flexible tape formed of a sandwich of Mylar film, metal foil and a flexible spacer having an adhesive on one side. The tape may be adhered directly to the bottom of a parking gate for use as a sensor. Also disclosed is a nonconductive sleeve member for use with a tubular metal arm to permit attachment of the sensor directly to the distal end of the arm. In another embodiment, the sensor is mounted to an object with a spacer. The spacer has a body with a low dielectric constant to space the sensor a predetermined distance from a conductive material such as a garage door.